The invention relates to a steering wheel having an air-bag module in accordance with the preamble of claim 1.
In the case of motor-vehicle steering wheels, because of the rigid coupling to the steering column there is the problem of a steering wheel vibrating at least in certain speed ranges. These vibrations are caused as a function of a certain rotational speed of the engine by the characteristic frequency of the air-bag steering wheel. In order to reduce these vibrations, in addition to shifting the characteristic frequency of the air-bag steering wheel, by attaching an additional mass to the steering wheel, into a frequency range lying outside the range of the oscillations actually occurring on the steering wheel, it is disclosed, for example, in DE 37 10 173 A1 to mount the housing of the air-bag unit on the steering wheel in a damped manner in terms of oscillations in such a manner that the said housing can be moved relative to the steering wheel and transverse to the longitudinal axis of the steering column. Provision is additionally made for the housing also to be movable in the direction of the longitudinal axis of the steering column. Its ability to move is achieved by holding clips having bearing bushings, which have noise-damping properties, in corresponding holes being arranged at the sides of the housing. Holding screws for fastening the holding clips to the spokes of the steering wheel are guided through the bearing bushings. In this arrangement, there is a clearance between the shank of each holding screw and the respective bushing, the said clearance enabling the holding clips to be shifted laterally with respect to the holding screws. A floating mounting arrangement is therefore obtained. In this case, the entire air-bag module, including the cap, which screens the module off from the passenger compartment, is mounted in a floating manner.
The disadvantage of this arrangement resides in the fact that when vibrations occur at the steering wheel, these vibrations can be seen, inter alia, because of the relative movement of the cap with respect to the steering wheel. This is because while the steering wheel oscillates as a consequence of the rigid coupling to the steering spindle, greatly reduced vibrations, if any at all, occur at the cap. There must therefore be a relatively large gap between the cap and the steering wheel in order to avoid the mutual friction and therefore annoying noises when vibrations occur.
Furthermore, DE 39 25 761 A1 discloses a vibration-suppressing device for a steering wheel having an air-bag module. In this device, a housing for holding the air bag is attached rigidly to the steering-wheel body and the gas generator is attached to the housing by a plurality of elastic means. Elastic bushings which are held by means of rivets are provided as the elastic means.
The disadvantage of this arrangement is that after the gas generator is ignited, gas can not only flow into the air bag, but can also flow in the opposite direction out of the steering wheel, with the result that the pressure in the air bag is reduced as is therefore the pressure for opening the covering cap.
The invention is based on the object of damping oscillations at the steering wheel to the greatest possible extent and of obtaining an improved cap-opening pressure.
In the case of a steering wheel having an air-bag module which has a gas generator and an air bag and is covered with respect to the passenger compartment by means of a covering cap provided on the upper side of the steering wheel, the gas generator being provided as an oscillation damper by being mounted in the air-bag module in at least one element which is elastically deformable when the steering wheel oscillates, the gas generator is peripherally mounted in the elastically deformable element and/or the elastically deformable element has a peripheral sealing lip which, after the gas generator is ignited, bears against the latter or against a component connected to the latter.
This results in the advantage that, in spite of a covering cap which moves separately from the steering wheel on the upper side of the steering wheel, because of the oscillation damping a relative movement between the covering cap and the steering wheel is at least reduced. Even in the case of a steering wheel with an integrated air bag where the covering cap is part of the steering wheel, the oscillation damping on the steering wheel is effective in the same manner. At the same time, a sealing function is obtained because of the peripheral mounting arrangement of the gas generator. In the design with a sealing lip, the latter, in the inoperative state, does not bear [lacuna] gas generator or against a component connected to the latter so as not to affect the function of the gas generator as an oscillation damper. Only after the gas generator is ignited is the sealing lip placed into position giving rise to an increased pressure for opening the covering cap, since gas is prevented from flowing off counter to the unfolding direction of the air bag.
The elastically deformable element is expediently connected to the air-bag module by means of at least one additional component.
The additional component can consist, for example, of plastic or sheet metal.
In one embodiment, the elastically deformable element is fixed within the air-bag module by sheet-metal parts of the air-bag module. In a further refinement, provision is made for the air bag, a diffuser and the covering cap to be fastened to at least one of the sheet-metal parts. The diffuser also prevents, inter alia, contact between the air bag and the gas generator, so that oscillations of the said gas generator cannot be transmitted to the air bag.
In one embodiment, at least one first sheet-metal part is connected to the steering wheel and this sheet-metal part has a depression in which a side edge of the covering cap engages. Furthermore, at least one second sheet-metal part is connected to the first sheet-metal part via this side edge.
The fastening of the gas generator expediently takes place in such a manner that a flange of the gas generator engages in the elastically deformable element.
In a further embodiment, provision is made for the air bag to be fastened together with a diffuser to the air-bag module.
In one embodiment, the elastically deformable element has a downwardly pointing peg. The latter facilitates the positioning of the gas generator and assists in the function of the gas generator as an oscillation damper. In order to obtain simple installation of the pegs, the latter are expediently provided with an introducing bevel.
A groove is preferably provided on the elastically deformable element for receiving the flange of the gas generator, the groove bottom being curved outwards and the groove side surfaces diverging therefrom.
An oscillating element made of rubber is preferably provided as the elastically deformable element.
The arrangement according to the invention can be used both in a steering wheel with an integrated air bag where the covering cap is part of the steering wheel, and in a design where a covering cap which moves separately from the steering wheel is provided.
Furthermore, in one design, in addition to the elastic mounting arrangement of the gas generator the air-bag module as a whole is additionally spring-mounted, with the result that a floating horn device can be provided, whereby the horn contacts can therefore be closed by pressing down the covering cap or one of the regions thereof.
A cup-shaped gas generator is preferably provided as the gas generator.